CN109643891B

CN109643891B - System and method for fault interruption using MEMS switches

Info

Publication number: CN109643891B
Application number: CN201780040548.0A
Authority: CN
Inventors: S·E·韦弗; R·圣-皮埃尔; G·S·克莱登
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2016-06-29
Filing date: 2017-06-27
Publication date: 2020-02-14
Anticipated expiration: 2037-06-27
Also published as: TWI742099B; JP7018904B2; US20180006445A1; CN109643891A; US10211622B2; EP3479449B1; JP2019520679A; WO2018005520A1; EP3479449A1; TW201810852A

Abstract

An electrical system includes an operating MEMS switch operable in on and off states to enable and disable current flow to a load and a fault interrupting MEMS switch positioned in series with the operating MEMS switch. The fault interrupting MEMS switch is operable in on and off states to enable current flow to the electrical load and to inhibit current flow to the electrical load, wherein operation of the fault interrupting MEMS switch in the off state inhibits current flow to the load regardless of the state of the operating MEMS switch. The fault sensor controls operation of the system to sense a system variable, analyze the system variable to detect whether a fault is affecting the electrical system, and upon detection of the fault, switch the fault interrupting MEMS switch from an on state to an off state to interrupt current flow to the load by operating the MEMS switch.

Description

System and method for fault interruption using MEMS switches

Background

Embodiments of the present invention relate generally to Micro-Electro-Mechanical System (MEMS) switches and, more particularly, to systems and methods for fault interruption using MEMS switches.

MEMS is a technology that, in its most general form, can be defined as miniaturized mechanical and electromechanical elements (i.e., devices and structures) made using microfabrication techniques. The critical physical dimensions of MEMS devices can vary from well below one micron to several millimeters at the lower end of the size spectrum. Also, the type of MEMS device can vary from a relatively simple structure without any moving elements to an extremely complex electromechanical system with multiple moving elements under the control of integrated microelectronics, where free-standing MEMS structures or "beams" often act as relays, for example.

With respect to MEMS devices having a moving element, such a moving element may be in the form of a free standing and suspended MEMS structure configured as a cantilever with a first end anchored to a substrate (e.g., fused silica, glass, silicon substrate), and a second free end having a contact. When the MEMS device is energized, the free-standing MEMS structure moves its contacts against the device substrate and substrate contacts below the MEMS structure contacts.

With particular regard to MEMS devices, it is also recognized that, in operation, contact of a free-standing structure with a substrate contact may cause the free-standing structure (i.e., the free-standing structure's contact) to experience mechanical wear due to: repeated physical impacts with the substrate contact, heating of the free-standing structure contact by joule heating, and electrical discharges between the free-standing structure contact and the substrate contact. Such wear of the free-standing structure contacts may ultimately lead to reliability problems in the MEMS switch.

One common reliability problem in MEMS switches due to wear of free-standing structure contacts is that the contacts become stuck closed. Other conditions that may cause a stuck-closed contact failure mode are arcing due to hot-switching conditions, stiction due to de-watts forces (van der Waals force), plastic deformation of the beam, or gate driver failure when the MEMS device is in an on condition. Depending on the system in which the MEMS switch is installed, a stuck-closed fault condition may cause more failures upstream or downstream of the stuck MEMS switch, and may be particularly problematic in applications involving a large number of MEMS switches.

It is to be appreciated that the stuck-closed failure mode in the MEMS switch is not the only failure mode that may occur in an electrical system. Other failure modes include, for example, short circuits, open circuits, voltage transients or power spikes, power faults, power sags, under or under voltage conditions, over voltage conditions, power line noise, frequency variations, switching transients, harmonic distortion, and cooling system failures. As with the stuck-closed failure mode in MEMS switches, any of the above listed failures can cause damage to the system if not properly detected and managed.

Accordingly, it is desirable to provide a fast acting and cost effective solution to interrupt the circuitry of a MEMS switch included in an electrical system that is experiencing a failure.

Disclosure of Invention

According to one aspect of the present invention, an electrical system having a fault interrupting MEMS switch unit includes a first operating MEMS switch in a first electrical path operable in an on state to enable current flow to a first electrical load and an off state to inhibit current flow to the first electrical load. The electrical system further includes a first fault interrupting MEMS switch positioned in series with the first operating MEMS switch, the first fault interrupting MEMS switch operable in an on state to enable current flow to the first electrical load and an off state to inhibit current flow to the first electrical load, wherein operation of the first fault interrupting MEMS switch in the off state inhibits current flow to the first electrical load regardless of the state of the first operating MEMS switch. The electrical system further includes a first fault sensor positioned to sense a first system variable; and a control system programmed to: receiving the first system variable from the first fault sensor; analyzing the first system variable to detect whether a fault is affecting the electrical system; and upon detection of a fault, switching the first fault interrupting MEMS switch from the on state to the off state to interrupt current flow through the first operating MEMS switch to the first electrical load.

According to another aspect of the invention, a method of interrupting current in a circuit upon detection of a fault condition includes: receiving power at an input of the circuit; and closing, by the controller, a first fault isolating MEMS switch upon energizing the circuit so as to allow current to flow from the input to a first circuit load, the first fault isolating MEMS switch positioned in a first current path. The method further includes selectively operating a first operating MEMS switch in series with the first fault isolating MEMS switch to provide current to the first circuit load through the first current path and to interrupt current through the first current path; measuring, by a first fault sensor, a first characteristic that is affecting the circuit; and providing the measured first characteristic to the controller. The method further includes monitoring, by the controller, the measured first characteristic to detect whether a fault condition exists; and upon detecting the presence of a fault condition, opening, by the controller, the first fault isolation MEMS switch to interrupt current flow to the first electrical load and prevent damage to the circuit.

According to yet another aspect of the invention, a power system with MEMS switch failure protection comprises: a power source; a first system load receiving power from the power source; and a first process MEMS switch disposed along a first circuit path between the power source and the first system load, the first process MEMS switch operable in a closed position and an open position to selectively control current flow from the power source to the first system load. The power system further includes a fail-safe MEMS switch module having: a first fail-safe MEMS switch positioned in series with the first process MEMS switch, the first fail-safe MEMS switch operable in a closed position and an open position to selectively control current flow through the first process MEMS switch; a first failure sensor to measure a first system characteristic corresponding to a position of the first process MEMS switch; and a control unit programmed to: receiving the first system characteristic from the first failure sensor; determining whether the first process MEMS switch is stuck in the closed position using the first system characteristic; and upon determining that the first process MEMS switch is stuck in the closed position, switching the first fail-safe MEMS switch from the closed position to the open position to electrically isolate the first system load from the power source.

Various other features and advantages will be apparent from the following detailed description and drawings.

Drawings

The drawings illustrate embodiments presently contemplated for carrying out the invention.

In the drawings:

fig. 1 is a schematic perspective view of a MEMS switch according to an exemplary embodiment of the invention.

Fig. 2 is a schematic side view of the MEMS switch of fig. 1 in an open position.

Fig. 3 is a schematic side view of the MEMS switch of fig. 1 in a closed position.

Fig. 4 is a schematic diagram of a power system incorporating a fault interrupting MEMS switch module, in accordance with an embodiment of the present invention.

Fig. 5 is a schematic diagram of a power system incorporating a fault interrupting MEMS switch module according to another embodiment of the present invention.

Detailed Description

Embodiments of the invention set forth herein relate to interrupting power or a circuit or system during a fault condition or failure mode using a MEMS switch. A fault or failure interrupting or isolating MEMS switch module is provided that includes a fault or failure interrupting or isolating MEMS switch for interrupting a power or electrical system or circuit during a fault to isolate a power source from an electrical load. Upon system power-up or startup, a control system in the MEMS switch module closes the fault interrupting MEMS switch and opens the fault interrupting MEMS switch based on feedback from a fault or failure sensor that measures a characteristic or variable that is representative of whether a fault condition has occurred.

Referring to fig. 1-3, schematic perspective views of an electrostatic micro-electromechanical system (MEMS) switch 10 according to an exemplary embodiment of the present invention are shown. According to the exemplary embodiment shown in fig. 1-3, the MEMS switch 10 includes a substrate contact 12 comprising a conductive material (e.g., a metal). The MEMS device 10 also includes free-standing and suspended MEMS structures 14 that include free-standing structures/mechanical elements 16, such as beams, where the free-standing structures 16 have cantilever portions 18 that extend above the contacts 12, and a bottom side or surface 17 of the free-standing structures 16 is covered in an exemplary embodiment by a seed layer 20 that is mechanically coupled to and electrically connected to the structures, as will be discussed in more detail below. The free-standing structure 16 is supported by an anchor portion 22, the cantilever portion 18 extending from the anchor portion 22, and the anchor portion 22 may be integrated with the free-standing structure 16. The anchor portions 22 are used to connect the cantilever portions 18 of the free-standing structure 16 to an underlying support structure, such as a conductive mount 21 formed on a substrate 24. The substrate 24 may be formed from any of a wide variety of materials suitable for MEMS device fabrication, including, for example, silicon and silicon-based substrates (e.g., silicon carbide (SiC)), fused silica, or glass.

As shown in fig. 2 and 3, the free-standing structures 16 may be configured to be selectively movable between a first non-contacting, off, or open position or state shown in fig. 2, in which the free-standing structures 16 (and seed layer 20) are separated from the contacts 12 by a separation distance d, and a second contacting, on, or closed position or state shown in fig. 3, in which the free-standing structures 16 (and seed layer 20) form electrical contact with the contacts 12. As shown, seed layer 20 serves as an electrical contact for free-standing structure 16. Thus, when seed layer 20 makes mechanical contact and electrical communication with electrical contact 12, seed layer 20 electrically couples free-standing structure 16 and contact 12. Moreover, free-standing structures 16 and seed layer 20 can be configured to undergo deformation when moved between the contact position and the non-contact position, such that free-standing structures 16 and seed layer 20 are naturally disposed (i.e., in the absence of an externally applied force) in the non-contact position and can deform so as to occupy the contact position while storing mechanical energy therein. In other embodiments, the undeformed configuration of free-standing structures 16 and seed layer 20 may be contact locations.

Referring again to FIG. 1, the MEMS switch 10 may also include electrodes26, electrode 26, when properly charged, provides a potential difference between electrode 26 and free-standing structures 16 and seed layer 20, causing electrostatic forces to pull free-standing structures 16 and seed layer 20 toward electrode 26 and against contact 12. Sufficient voltage is applied to electrodes 26 and electrostatic forces deform free-standing structures 16 and seed layer 20, thereby displacing free-standing structures 16 and seed layer 20 from the non-contacting (i.e., open or non-conductive) position shown in fig. 2 to the contacting (i.e., closed or conductive) position shown in fig. 3. Thus, the electrode 26 may act as a "gate" for the MEMS switch 10, wherein a voltage applied to the electrode 26 (referred to as a "gate voltage") is used to control the opening or closing of the MEMS structure 14. The electrode 26 may be in communication with a gate voltage source 28 such that the gate voltage V_GMay be selectively applied to the electrodes 26.

Contacts 12, free-standing structures 16, and seed layer 20 are components of circuit 30. The exemplary circuit 30 has a first side 32 and a second side 34 that are at different potentials relative to each other (since only one side is connected to the power source 36) when the first side 32 and the second side 34 are disconnected from each other. Contacts 12 and free-standing structures 16 may be connected to either side 32, 34, respectively, of circuit 30 through seed layer 20, such that deformation of free-standing structures 16 and seed layer 20 between the first and second positions serves to pass and interrupt, respectively, current therethrough. The free-standing structures 16 and seed layer 20 may be repeatedly moved into and out of contact with the contacts 12 at a frequency determined by the application for which the MEMS structure 14 is used (either uniformly or non-uniformly). When contacts 12 and bottom surfaces 17 of free-standing structures 16, including seed layer 20, are spaced apart from each other, the voltage difference between contacts 12 and free-standing structures 16 is referred to as a "stand-off voltage".

In one embodiment, free-standing structures 16 and seed layer 20 may be in communication with power supply 36 (e.g., via anchor structure 22), and contact 12 may have a load resistance R_LIs connected to the electrical load 38. The power supply 36 may operate as a voltage source or a current source. Free-standing structures 16 and seed layer 20 act as electrical contacts (i.e., ohmic contacts) such that a load current passes from power supply 36 through free-standing structures 16 and seed layer 2 when free-standing structures 16 and seed layer 20 are in a contact position0 flow into contact 12 and toward electrical load 38, otherwise interrupting or interrupting the electrical path and preventing current flow from the power source to the load when free-standing structure 16 and seed layer 20 are in a non-contacting position.

The MEMS structure 14 described above may be used as part of an electrical or power system or circuit that includes other switching structures, whether similar or dissimilar in design, in order to improve the current and voltage capabilities of the overall circuit. Such switch structures may be configured in series or in parallel to facilitate even distribution of isolation voltage when the switch structure is open and even distribution of current when the switch structure is closed.

Referring now to fig. 4, a schematic diagram of an electrical or power system or circuit 42 incorporating a fault or failure interrupt or isolation MEMS switch module or unit 44 is shown, in accordance with an embodiment of the present invention. The fault interrupting MEMS switch module 44 protects the power system 42 during fault conditions or failure modes by interrupting current flow through the power system 42 and isolating each electrical load from each power source. The MEMS switch module 44 includes a fault or failure isolation or interruption MEMS switch 46, a fault or failure sensor 48, and a control system or unit 50 that controls the fault interruption MEMS switch 46 based on measured or sensed circuit or system characteristics or variables received from the fault sensor 48. The power system 42 also includes a power source or system, circuit or electrical load 52 and a power source or system, circuit or electrical load 54 along a current or electrical path 56. Electrical path 56 electrically connects or couples source or load 52 to source or load 54 through fault interrupt MEMS switch 46 and operation or process MEMS switch 58.

The power system 42 may also include an optional power source, circuit, or electrical load 60. Although two optional sources or loads 60 are shown, power system 42 should not be limited to four sources or loads 52, 54, 60 and may include additional sources or loads as desired. If power system 42 includes an optional source or load 60, optional source or load 60 is electrically connected or coupled to source or load 54 through fault interrupt MEMS switch 46 and additional operational or process MEMS switch 58 along electrical current or

electrical paths

62, 64. In some embodiments, the control system 50 controls the process MEMS switch 58 according to conventional operation of the power system 42. In other embodiments, another control system or unit (not shown) controls process MEMS switch 58 according to conventional operation of power system 42. The fault interrupting MEMS switch module 44 may also include an optional fault or failure sensor 66 along the

electrical paths

62, 64 in communication with the control system 50.

Although

reference numerals

52 and 54 indicate sources or loads, one of the source or load 52 and the source or load 54 will be a source and one of the source or load 52 and the source or load 54 will be a load. For example, in one embodiment, source or load 52 is a power source and source or load 54 is an electrical load. In another embodiment, source or load 54 is a power source and source or load 52 is an electrical load. Likewise, if an optional source or load 60 is included in power system 42, source or load 60 will follow source or load 52 such that source or load 60 is the source if source or load 52 is the source and source or load 60 is the load if source or load 52 is the load. For example, in one embodiment, source or load 52 and source or load 60 are power sources, and source or load 54 is an electrical load. In another embodiment, source or load 54 is a power source and source or load 52 and source or load 60 are electrical loads. In any event, each

current path

56, 62, 64 extends through the fault interrupting MEMS switch 46. Further, the process MEMS switches 58 can be implemented as individual switches or as an array of switches.

The fault interrupting MEMS switch 46 and the process MEMS switch 58 may each be in the form of an electrostatic MEMS switch such as, for example, the MEMS switch 10 of fig. 1. Further, each

MEMS switch

46, 58 is operable in an open or off state or position that prevents or inhibits current flow therethrough and a closed or on state or position that permits or enables current flow therethrough. Example open and closed positions of a MEMS switch are shown in fig. 2 and 3, respectively. Moreover, if the fault interrupting MEMS switch 46 is identically constructed to the process MEMS switch 58, the fault interrupting MEMS switch 46 and any corresponding interconnect circuitry may be constructed in parallel on the same monolithic substrate as the process MEMS switch 58, such that the fault interrupting MEMS switch 46 and the process MEMS switch are part of the same switch architecture, and the additional fault interrupting MEMS switch 46 adds little or no cost to the construction of the power system 42.

As described above, the MEMS switch module 44 operates to protect the power system 42 in the event of a fault or failure that may cause damage to, or at least affect the performance of, the power system 42. Once the system is powered on, the control system 50 switches the fault interrupting MEMS switch 46 from the open position to the closed position so that the source or load 52 can be electrically coupled or connected to the source or load 54. If the fault interrupting MEMS switch 46 is in the form of the electrostatic MEMS switch 10 of FIG. 1, the control system 50 closes the MEMS switch 46 by applying a gate voltage to the electrode 26 that is large enough to pull the free-standing structure 16 toward the contact 12 as shown in FIG. 3. Fault sensors 48 and, if included in MEMS switch module 44, each optional fault sensor 66 measures or senses one or more system or circuit characteristics or variables.

Although

fault sensors

48, 66 are shown in fig. 4 as current sensors in

current paths

56, 62, 64,

fault sensors

48, 66 should not be limited to the current sensors shown,

current paths

56, 62, 64, or the number of

fault sensors

48, 66. The

fault sensors

48, 66 may be used to detect any type of variable that may be used to determine whether a fault condition is present in the power system 42, such as, for example, voltage, current, logic state, and temperature. Each

faulty sensor

48, 66 may be used to measure a different type of variable, or may be used in conjunction with other

faulty sensors

48, 66. In any case, the

fault sensors

48, 66 then communicate their measurements to the control system 50.

Control system 50 then analyzes or monitors the measured variables to determine or detect whether there are existing fault conditions that are affecting or may affect power system 42. One type of fault condition that control system 50 monitors is a stuck-closed condition during which process MEMS switch 58 is unable to open for the reasons previously described. In this case, the control system 50 may monitor the current in the

current paths

56, 62, 64 to detect whether the process MEMS switches 58 are closed when they should be open. However, the control system 50 may also analyze the additional/alternative variables set forth above for other fault conditions, such as, for example, short circuits, open circuits, voltage transients or power spikes, power faults, power sags, under or under voltage conditions, over voltage conditions, power line noise, frequency variations, switching transients, harmonic distortion, and cooling system failures. Control system 50 may use any number of measurements within or external to power system 42 to monitor any of the fault conditions mentioned above, where fig. 4 illustrates that power system 42 may be connected to an external system 65, and that external system 65 may have one or more optional fault sensors 67 for measuring one or more variables associated with any of the fault conditions described above. For example, the power system 42 may be connected to an external cooling system 65 having a fault sensor 67, the fault sensor 67 being used to sense a variable indicating whether the external cooling system has failed.

If the control system 50 determines that no fault condition exists, the control system 50 continues to hold the fault interrupting MEMS switch 46 in the closed position. However, if the control system 50 detects a fault condition, the control system 50 switches the fault interrupting MEMS switch 46 from the closed position to the open position to disable the source or load 52 from being electrically coupled or connected to the source or load 54. For example, if one or more process MEMS switches 58 are stuck in a closed position, the control system 50 will detect the stuck-closed condition and open the fault interrupting MEMS switch 46. If the fault interrupting MEMS switch 46 is in the form of the electrostatic MEMS switch 10 of FIG. 1, the control system 50 opens the MEMS switch 46 by stopping the application of the gate voltage to the electrode 26, such that the free-standing structure 16 is separated from the contact 12 as shown in FIG. 2.

When the fault interrupting MEMS switch 46 is in the open position, then no current may flow between the source or load 52 and the source or load 54 regardless of the position of the process MEMS switch 58. This is because each

current path

56, 62, 64 can only be completed when the fault interrupting MEMS switch 46 is in the closed position. Thus, switching the fault interrupting MEMS switch 46 from the closed position to the open position interrupts the power system 42 and isolates the source or load 54 from the sources or loads 52, 60. The isolation provided by the fault interrupting MEMS switch 46 prevents the power system 42 from incurring any further damage due to the fault condition. Also, because the fault interrupting MEMS switch 46 may only have to be opened once, the reliability of the fault interrupting MEMS switch 46 will far exceed the reliability of the process MEMS switch 58. This increased reliability of MEMS switch 46 benefits power system 42 because process MEMS switch 58 operates in a hot switching condition, which degrades its reliability much faster than a cold switching condition.

While it is recognized that fuses or transistors may be used in place of the fault interrupting MEMS switch 46, the fault interrupting MEMS switch 46 provides significant advantages over either fuses or transistors. Both fuses and transistors are less cost effective than the fault interrupting MEMS switch 46 because the fault isolating MEMS switch 46 and any corresponding interconnect circuitry as described above can be fabricated in parallel with the process MEMS switch 58 on the same monolithic substrate. In systems where fault interruption is required in many places (e.g., systems including tens, hundreds, or thousands of process MEMS switches), the fault interrupting MEMS switch 46 will be a significant cost savings. Also, the fuses would require manual reset as opposed to a system reset that could be performed on the fault interrupting MEMS switch 46. Also, the fuse will operate much slower than the fault interrupting MEMS switch 46. Further, as a mechanical relay, the fault interrupting MEMS switch 46 provides more isolation than a transistor that may experience leakage.

Referring now to fig. 5, a schematic diagram of an electrical or power system or circuit 68 incorporating a fault or failure interruption or isolation MEMS switch module or unit 70 is shown, according to another embodiment of the present invention. Power system 68 includes many components similar to the components of power system 42 of FIG. 4, and thus, the numbers used to refer to the components in FIG. 4 are also used to refer to similar components in FIG. 5. The fault interrupting MEMS switch module 72 protects the power system 68 during fault conditions or failure modes by interrupting current flow through the power system 68 and isolating each electrical load from each power source. The fault interrupting MEMS switch module 70 includes a fault or failure isolation or interrupting MEMS switch 46, a fault or failure sensor 48, and a control system or unit 72 that controls the fault interrupting MEMS switch 46 based on measured or sensed circuit or system characteristics or variables received from the fault sensor 48. The power system 68 also includes a power source or system, circuit or electrical load 74 and a power source or system, circuit or electrical load 76. The power system 68 may also include optional power sources, circuits, or

electrical loads

78,80,82, 84. Although only four optional sources or loads 78,80,82,84 are shown, power system 68 should not be limited to six sources or loads 74, 76, 78,80,82,84, and additional sources or loads may be included as desired.

As with the sources or loads 52, 54, 60 of fig. 4, the sources or loads 74, 76, 78,80,82,84 are configured such that the sources are electrically connected only to the loads and the loads are electrically connected only to the sources. The sources or loads 74, 76, 78,80,82,84 may be electrically connected or coupled to one another in a number of ways along current or

circuit paths

86, 88 and optional current or circuit path 90. However, although only one optional electrical path 90 is shown, power system 68 should not be limited to one optional electrical path 90 and may include additional electrical paths as desired.

The sources or loads 74, 78, 82 may be electrically coupled to one or all of the sources or loads 76, 80, 84 along separate, parallel, or independent

electrical paths

86, 88, 90 in any conceivable combination. For example, in one embodiment, power system 68 includes only sources or loads 74, 76, with sources or loads 74, 76 being electrically coupled to each other in a multi-phase power system by

electrical paths

86, 88 or

electrical paths

86, 88, 90. In another embodiment, the power system 68 includes only the sources or loads 74, 76, 78, 82, such that the sources or loads 74, 78, 82 are electrically coupled to the source or load 76 by

electrical paths

86, 88. In yet another example, power system 68 includes only sources or loads 74, 76, 78,80,82,84 such that source or load 74 is electrically coupled to source or load 76 by electrical path 86, source or load 78 is electrically coupled to source or load 80 by electrical path 88, and source or load 80 is electrically coupled to source or load 82 by electrical path 90. The above examples are not meant to be an exhaustive list of embodiments of power system 68, but are described for the purpose of illustrating possible electrical connections between sources or loads 74, 76, 78,80,82, 84.

In either case, each parallel

electrical path

86, 88, 90 includes the process MEMS switch 58 and the fault interrupting MEMS switch 46. In some embodiments, the control system 72 controls the process MEMS switch 58 according to conventional operation of the power system 68. In other embodiments, another control system or unit (not shown) controls process MEMS switch 58 according to conventional operation of power system 68. MEMS switch module 70 may include optional fault sensor 66 if power system 68 includes optional electrical path 90. As described with respect to the power system 42 of fig. 4, the fault interrupt MEMS switch 46 and the process MEMS switch 58 may each be in the form of an electrostatic MEMS switch, such as, for example, the MEMS switch 10 of fig. 1, and may be operable in an open or closed position, such as the open and closed positions shown in fig. 2 and 3, respectively. Further, as described with respect to the power system 42 of fig. 4, if the fault interrupting MEMS switch 46 is constructed the same as the process MEMS switch 58, the fault interrupting MEMS switch 46 may be constructed in parallel with the process MEMS switch 58 on the same monolithic substrate. The fault interrupting MEMS switch 46 and the process MEMS switch are then part of the same switch architecture, and the additional fault interrupting MEMS switch 46 adds little or no cost to the construction of the power system 68.

As explained above, the MEMS switch module 70 operates to prevent the power system 68 from continuing to experience damage due to a fault or failure that has occurred. When the power system 68 is energized, the control system 72 switches the fault interrupting MEMS switch 46 from the open position to the closed position such that the source or load 74 is electrically coupled to the source or load 76. If the fault interrupting MEMS switch 46 is in the form of the electrostatic MEMS switch 10 of FIG. 1, the control system 72 applies a sufficient gate voltage to the electrode 26 of the fault isolating MEMS switch 46 to pull the free-standing structure 16 toward the contact 12 as shown in FIG. 3. Fault sensors 48 and, if included in MEMS switch module 72, each optional fault sensor 66 measures or senses one or more system or circuit characteristics or variables.

Although

fault sensors

48, 66 are shown in fig. 5 as current sensors in

current paths

86, 88, 90, respectively,

fault sensors

48, 66 should not be limited to current sensors,

current paths

86, 88, 90, or the number of

fault sensors

48, 66 shown. The

fault sensors

48, 66 may be used to detect any type of variable that may be used to determine whether a fault condition has occurred, such as, for example, voltage, current, logic state, and temperature. Each

faulty sensor

faulty sensors

48, 66. In any event, the

fault sensors

48, 66 then communicate their measurements to the control system 72.

The control system 72 then analyzes or monitors the measured characteristics to determine or detect whether there are existing fault conditions that are affecting or may affect the power system 68. One type of fault condition that control system 50 monitors is a stuck-closed condition during which process MEMS switch 58 is unable to open for the reasons previously described. In this case, control system 72 may monitor the currents in

current paths

86, 88, 90 to detect whether process MEMS switches 58 are closed when they should be open. However, the control system 72 may also analyze the characteristics of other fault conditions, such as, for example, short circuits, open circuits, voltage transients or power spikes, power faults, power sags, under or under voltage conditions, over voltage conditions, power line noise, frequency variations, switching transients, harmonic distortion, and cooling system failures. Control system 72 may use any number of measurements made within or external to power system 68 to detect any of the above fault conditions. The power system 68 may be connected to an external system 92, and the external system 92 may have one or more optional fault sensors 94 for measuring one or more variables associated with any of the fault conditions described above. For example, the power system 68 may be connected to an external cooling system 92 having a fault sensor 94, the fault sensor 94 being used to sense a variable indicating whether the external cooling system has failed.

If the control system 72 does not detect a fault condition, the control system 72 maintains the fault interrupting MEMS switch 46 in the closed position. However, if the control system 72 determines that a fault condition has occurred, the control system 72 switches all of the fault interrupting MEMS switches 46 from the closed position to the open position to disable the source or load 74 from being electrically coupled to the source or load 76. For example, if one or more process MEMS switches 58 are stuck in a closed position, control system 72 will detect the stuck-closed condition and open each fault interrupting MEMS switch 46. If the fault interrupting MEMS switch 46 is in the form of the electrostatic MEMS switch 10 of FIG. 1, the control system 72 opens the MEMS switch 46 by stopping the application of the gate voltage to the electrode 26, such that the free-standing structure 16 is separated from the contacts 12 as shown in FIG. 2.

When the control system 72 opens the fault interrupt MEMS switch 46, current is prevented from flowing between the source or load 74 and the source or load 76 even though the process MEMS switch is in the closed position. This is because each

current path

86, 88, 90 is complete only when the fault interrupting MEMS switch 46 is closed. Thus, opening the fault interrupt MEMS switch 46 will interrupt the power system 68 and isolate the source or load 74 from the source or load 76. This isolation prevents the power system 68 from continuing to cause any further damage during the fault condition. Also, because the fault interrupting MEMS switch 46 may only have to be opened once, the fault interrupting MEMS switch 46 has a much higher reliability than the process MEMS switch 58. This increased reliability of MEMS switch 46 benefits power system 68 because process MEMS switch 58 operates in a hot switching condition, which degrades its reliability much faster than a cold switching condition.

Beneficially, embodiments of the present invention thus provide a power system including a fault interrupting MEMS switch module. The MEMS switch module includes a fault interrupting MEMS switch operated by the control system based on feedback from the at least one fault sensor. The control system closes the fault interrupting MEMS switch upon system power up and opens the fault interrupting MEMS switch upon detection of a fault condition, such as, for example, a stuck-closed condition in a process MEMS switch in a power system. When the fault interrupting MEMS switch is in the open position, no current can flow therethrough and the electrical loads in the power system are isolated from the power source. The fault interrupting MEMS switch and any corresponding interconnect circuitry may be constructed in the same MEMS switch architecture as other process MEMS switches in the power system, thus providing a low cost solution to interrupting fault conditions in the power system compared to, for example, fuses and transistors. Fault interrupting MEMS switches offer additional advantages over fuses and transistors in that they are fast acting, do not require manual reset, and provide physical, rather than electrical, isolation of the electrical load.

According to one embodiment of the present invention, an electrical system having a fault interrupting MEMS switch unit includes a first operating MEMS switch in a first electrical path operable in an on state to enable current flow to a first electrical load and an off state to inhibit current flow to the first electrical load. The electrical system further includes a first fault interrupting MEMS switch positioned in series with the first operating MEMS switch, the first fault interrupting MEMS switch operable in an on state to enable current flow to the first electrical load and an off state to inhibit current flow to the first electrical load, wherein operation of the first fault interrupting MEMS switch in the off state inhibits current flow to the first electrical load regardless of the state of the first operating MEMS switch. The electrical system also includes a first fault sensor positioned to sense a first system variable and a control system programmed to: receiving the first system variable from the first fault sensor; analyzing the first system variable to detect whether a fault is affecting the electrical system; and upon detection of a fault, switching the first fault interrupting MEMS switch from the on state to the off state to interrupt current flow through the first operating MEMS switch to the first electrical load.

According to another embodiment of the invention, a method of interrupting current in a circuit upon detection of a fault condition includes: the method includes receiving power at an input of the circuit and closing, by a controller, a first fault isolation MEMS switch positioned in a first current path upon energizing the circuit so as to allow current to flow from the input to a first circuit load. The method further includes selectively operating a first operating MEMS switch in series with the first fault isolating MEMS switch to provide current to the first circuit load through the first current path and to interrupt current flow through the first current path; measuring, by a first fault sensor, a first characteristic that is affecting the circuit; and providing the measured first characteristic to the controller. The method further includes monitoring, by the controller, the measured first characteristic to detect whether a fault condition exists; and upon detecting the presence of a fault condition, opening, by the controller, the first fault isolation MEMS switch to interrupt current flow to the first electrical load and prevent damage to the circuit.

According to yet another embodiment of the present invention, a power system with MEMS switch failure protection comprises: a power source, a first system load that receives power from the power source, and a first process MEMS switch disposed along a first circuit path between the power source and the first system load; the first process MEMS switch is operable in a closed position and an open position to selectively control current flow from the power source to the first system load. The power system further includes a fail-safe MEMS switch module having: a first fail-safe MEMS switch positioned in series with the first process MEMS switch and operable in a closed position and an open position to selectively control current flow through the first process MEMS switch; a first failure sensor to measure a first system characteristic corresponding to a position of the first process MEMS switch; and a control unit programmed to: receiving the first system characteristic from the first failure sensor; determining whether the first process MEMS switch is stuck in the closed position using the first system characteristic; and upon determining that the first process MEMS switch is stuck in the closed position, switching the first fail-safe MEMS switch from the closed position to the open position to electrically isolate the first system load from the power source.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. An electrical system (42, 68) having a fault interrupting micro-electromechanical system (MEMS) switch unit (44), the electrical system comprising:

a first operating MEMS switch (58) located in a first electrical path (56, 86), the first operating MEMS switch (58) operable in an on state to enable current flow to a first electrical load (54, 76) and an off state to inhibit current flow to the first electrical load (54, 76);

a first fault interrupting MEMS switch (46) positioned in series with the first operating MEMS switch (58), the first fault interrupting MEMS switch (46) operable in an on state that enables current flow to the first electrical load (54, 76) and an off state that inhibits current flow to the first electrical load (54, 76), wherein operation of the first fault interrupting MEMS switch (46) in the off state inhibits current flow to the first electrical load (54, 76) regardless of a state of the first operating MEMS switch (58);

a first fault sensor (48), the first fault sensor (48) positioned to sense a first system variable; and

a control system (50, 70), the control system (50, 70) programmed to:

receiving the first system variable from the first fault sensor (48);

analyzing the first system variable to detect whether a fault is affecting the electrical system (42, 68); and

upon detection of a fault, switching the first fault interrupting MEMS switch (46) from the on state to the off state to interrupt current flow through the first operating MEMS switch (58) to the first electrical load (54, 76).

2. The electrical system of claim 1, further comprising a second fault sensor (48), the second fault sensor (48) positioned to sense a second system variable; and

wherein the control system (50, 70) is further programmed to:

receiving the second system variable from the second fault sensor (48);

analyzing the second system variable to detect whether a fault is affecting the electrical system (42, 68); and

upon detection of a fault based on analysis of any of the first and second system variables, the first fault interrupting MEMS switch (46) is switched from the on state to the off state to interrupt current flow through the first operating MEMS switch (58) to the first electrical load (54, 76).

3. The electrical system of claim 1, further comprising a second operating MEMS switch (58) positioned in a second electrical path (62) and in series with the first fault interrupting MEMS switch (46), the second operating MEMS switch (58) operable in an on state that enables current flow to the first electrical load (54) and an off state that inhibits current flow to the first electrical load (54); and is

Wherein when the first fault interrupting MEMS switch (46) is in the off state, current flow to the electrical load (54) is inhibited regardless of the state of the second operating MEMS switch (58).

4. The electrical system of claim 1, further comprising:

a second operating MEMS switch (58) located in a second electrical path (88) different from the first electrical path (86), the second operating MEMS switch (58) operable in an on state to enable current flow to a first electrical load (76) and an off state to inhibit current flow to the first electrical load (76); and

a second fault interrupting MEMS switch (46) positioned in series with the second operating MEMS switch (58), the second fault interrupting MEMS switch (46) including an on state that enables current flow to the first electrical load (76) and an off state that inhibits current flow to the first electrical load (76) regardless of a state of the second operating MEMS switch (58); and is

Wherein the control system (70) is further programmed to switch the second fault interrupting MEMS switch (46) from the on state to the off state upon detection of a fault to interrupt current flow through the first and second operating MEMS switches (58) to the first electrical load (76).

5. The electrical system of claim 1, further comprising a second operating MEMS switch (58) positioned in a second electrical path (88) in parallel with the first electrical path (86), the second operating MEMS switch (58) operable in an on state to enable current flow to a second electrical load (80) and an off state to inhibit current flow to the second electrical load (80);

further comprising a second fault interrupting MEMS switch (46) positioned in series with the second operating MEMS switch (58), the second fault interrupting MEMS switch (46) comprising an on state that enables current flow to the second electrical load (80) and an off state that inhibits current flow to the second electrical load (80) regardless of a state of the second operating MEMS switch (58); and is

Wherein the control system (70) is further programmed to switch the second fault interrupting MEMS switch (46) from the on state to the off state upon detection of a fault to interrupt current flow through the first and second operating MEMS switches (58) to the first electrical load (80).

6. The electrical system of claim 1, wherein the control system (50, 70) is programmed to:

analyzing the first system variable to determine whether the first operating MEMS switch (58) is stuck in the conductive state; and

switching the first fault interrupting MEMS switch (46) from the on state to the off state upon determining that the first operating MEMS switch (58) is stuck in the on state.

7. The electrical system of claim 1, wherein the control system is further programmed to operate the first fault interrupting MEMS switch (46) in the conductive state upon startup of the electrical system (42, 68).

8. The electrical system of claim 1, wherein the control system (50, 70) is programmed to analyze the first system variable to detect whether one of a short circuit, an open circuit, a power surge, a power fault, a power sag, an under-voltage condition, an over-voltage condition, power line noise, a frequency change, a switching transient, a harmonic distortion, and a cooling system failure is affecting the electrical system.

9. The electrical system of claim 1, wherein the operating MEMS switch (58) and the fault interrupting MEMS switch (46) are constructed in parallel on a single monolithic substrate along with any interconnecting circuitry between the MEMS switch (58) and the fault interrupting MEMS switch (46).

10. A method of interrupting current in a circuit (42, 68) upon detection of a fault condition, the method comprising:

receiving power at an input of the circuit (42, 68);

closing, by a controller (50, 70), a first fault isolating MEMS switch (46) upon energizing the circuit (42, 68) so as to allow current to flow from the input to a first circuit load (54, 76), the first fault isolating MEMS switch (46) positioned in a first current path (56, 86);

selectively operating a first operating MEMS switch in series with the first fault isolating MEMS switch (46) to provide current to the first circuit load (54, 76) through the first current path (56, 86) and to interrupt current through the first current path (56, 86);

measuring a first characteristic affecting the circuit (42, 68) by a first fault sensor (48);

providing the measured first characteristic to the controller (50, 70);

monitoring, by the controller (50, 70), the measured first characteristic to detect whether a fault condition exists; and

upon detecting the presence of a fault condition, opening, by the controller (50, 70), the first fault isolation MEMS switch (46) to interrupt current flow to the first electrical load (54, 76) and prevent damage to the electrical circuit (42, 68).

11. The method of claim 10, wherein monitoring the measured first characteristic to detect whether a fault condition exists includes determining whether the measured first operational characteristic indicates that the first operational MEMS switch (58) is stuck in a closed position.

12. The method of claim 10, further comprising:

closing, by the controller (70), a second fault isolating MEMS switch (46) upon energizing the circuit (68) so as to allow current to flow from the input to a first circuit load (76), the second fault isolating MEMS switch (46) positioned in a second current path (88) in parallel with the first current path (86);

selectively operating a second operating MEMS switch (58) in series with the second fault isolating MEMS switch (46) to provide current to the first circuit load (76) through the second current path (88) and to interrupt current through the second current path (88); and

upon detecting the presence of a fault condition, opening, by the controller (70), the second fault isolation MEMS switch (46) to interrupt current flow to the first electrical load (76) and prevent damage to the electrical circuit (68).

13. The method of claim 10, further comprising:

closing, by the controller (70), a second fault isolation MEMS switch (46) upon energizing the circuit (68) so as to allow current to flow from the input to a second circuit load (80);

selectively operating a second operating MEMS switch (58) in series with the second fault isolating MEMS switch (46) to provide current to the second circuit load (80); and

upon detecting the presence of a fault condition, opening, by the controller (70), the second fault isolating MEMS switch (46) to interrupt current flow to the first electrical load (80) and prevent damage to the electrical circuit.

14. The method of claim 10, further comprising:

measuring a second characteristic affecting the circuit (42, 68) by a second fault sensor (48);

providing the measured second characteristic to the controller (50, 70); and

monitoring, by the controller (50, 70), the measured second characteristic to detect whether a fault condition exists.

15. The method of claim 10, wherein closing the first fault isolating MEMS switch (46) comprises applying a gate voltage to an electrode (26) sufficient to pull a free standing structure (16) electrically coupled to the input toward a contact (12) electrically coupled to the first electrical load (54, 76); and is

Wherein opening the first fault isolating MEMS switch (46) includes removing the gate voltage from the electrode (26) such that the free-standing structure (16) moves away from the contact (12).